In the manufacture of an electronic device such as a semiconductor device, a processing apparatus for processing a processing target object is used. Generally, the processing apparatus includes a processing vessel and a mounting table. The processing target object is carried into the processing vessel by a transfer device and mounted on the mounting table. Then, the processing target objet is processed within the processing vessel.
The position of the processing target object on the mounting table is an important factor to satisfy various requirements such as processing uniformity within a surface of the processing target object. Accordingly, the transfer device needs to transfer the processing target object to a preset position on the mounting table. If the transfer position of the processing target object by the transfer device is deviated from the preset position, coordinate information specifying a transfer destination of the transfer device needs to be corrected.
To correct the coordinate information of the transfer device, the position of the processing target object on the mounting table needs to be detected. Conventionally, an electrostatic capacitance sensor has been used for this detection. The detection of the position with the electrostatic capacitance sensor is described in Patent Document 1, for example.
Patent Document 1: Japanese Patent No. 4,956,328
In a processing apparatus such as a plasma processing apparatus, there is provided a mounting table having an electrostatic chuck configured to attract and hold a processing target object. Further, a focus ring is provided on the mounting table to surround an edge of the processing target object.
FIG. 1 is a cross sectional view illustrating an example configuration of the electrostatic chuck and the focus ring. As depicted in FIG. 1, an electrostatic chuck ESC has a substantially disk shape. A focus ring FR is extended in a circumferential direction with respect to a central axis AXE of the electrostatic chuck ESC to surround the electrostatic chuck ESC. The focus ring FR includes a first portion P1 and a second portion P2. Each of the first potion P1 and the second portion P2 has a circular plate shape. The second portion P2 is provided on the first portion P1. An inner periphery P2i of the second portion P2 has a diameter larger than a diameter of an inner periphery P1i of the first portion P1. A processing target object (wafer W in FIG. 1) is mounted on the electrostatic chuck ESC such that an edge region thereof is located above the first portion P1 of the focus ring FR.
In the configuration using the electrostatic chuck ESC and the focus ring FR as stated above, if a distance (gap) between an edge of the processing target object and the inner periphery P2i of the second portion P2 of the focus ring FR is not uniform in the circumferential direction, plasma distribution becomes non-uniform, so that non-uniformity in characteristics, such as fluctuation of an etching dimension within a surface of the processing target object is generated. Furthermore, local adhesion of particles to the processing target object may also occur. Thus, the coordinate information of the transfer device, that is, the coordinate information of the transfer destination of the processing target object needs to be corrected such that the distance between the edge of the processing target object and the inner periphery P2i of the second portion P2 of the focus ring FR is substantially uniform in the circumferential direction. For this purpose, the distance between the edge of the processing target object and the inner periphery P2i of the second portion P2 of the focus ring FR needs to be measured.
In this regard, the present inventors have been developing a technique in which a sensor chip for measuring electrostatic capacitance as a physical amount that reflects the distance is mounted on a measuring device having the same shape as the processing target object, the measuring device is transferred onto the electrostatic chuck by the transfer device, and the electrostatic capacitance is acquired by the measuring device. FIG. 2 provides a longitudinal cross sectional view illustrating an example structure of the sensor chip for measuring the electrostatic capacitance. A sensor chip 1000 shown in FIG. 2 is an example of a sensor chip capable of being mounted along an edge of the measuring device having the same shape as the processing target object. The sensor chip 1000 includes a substrate member 1002 and an electrode 1004. The substrate member 1002 has a main body 1002m. The main body 1002m is made of, for example, silicon and an insulating region 1002f is formed on a surface of the main body 1002m. The insulating region 1002f is, for example, a thermal oxide film. The substrate member 1002 has a top surface 1002a, a bottom surface 1002b and an end surface 1002c. The end surface 1002c has a step shape, and a lower portion 1002d of the end surface 1002c protrudes toward the focus ring FR more than an upper portion 1002u of the end surface 1002c. The electrode 1004 is provided along the upper portion 1002u of the end surface 1002c. 
FIG. 3 shows electrostatic capacitance measured by connecting the electrode of the sensor chip of FIG. 2 to an electrostatic capacitance meter. The electrostatic capacitance is measured while moving the sensor chip 1000 in a direction RD (FIG. 2) toward the inner periphery P2i of the second portion P2 of the focus ring FR. Further, when measuring the electrostatic capacitance, a distance LVD (FIG. 2) between a top surface Pit of the first portion P1 and the bottom surface of the sensor chip 1000 is 100 μm. In FIG. 3, a horizontal axis represents a distance LRD (FIG. 2) between the lower portion 1002d of the end surface 1002c of the substrate member 1002 and the inner periphery P2i of the second portion P2 of the focus ring FR, and a vertical axis indicates electrostatic capacitance. Further, FIG. 3 depicts both a calculation value of the electrostatic capacitance calculated by assuming that the electrostatic capacitance exists only in the direction RD and an actual measurement value of the electrostatic capacitance measured by the sensor chip 1000.
In comparison of the actual measurement value and the calculation value of the electrostatic capacitance shown in FIG. 3, the electrostatic capacitance (actual measurement value) measured by the sensor chip 1000 is found to sharply increase when the distance LRD is about 2.5 mm. This distance LRD of 2.5 mm is equal to a distance L12 (FIG. 2) between the inner periphery P2i of the second portion P2 and the inner periphery P1i of the first portion P1. Accordingly, this phenomenon implies that not only the electrostatic capacitance in the specific direction (direction RD of FIG. 2) in which the inner periphery (inner periphery P2i of the second portion P2) of the focus ring FR is provided with respect to the electrode 1004 of the sensor chip 1000, but electrostatic capacitance in a downward direction (direction VD of FIG. 2) also affects the measurement by the sensor chip 1000. In obtaining the distance LRD between the inner periphery of the focus ring FR and the sensor chip 1000, however, the electrostatic capacitance in the downward direction of the sensor chip 1000 is unnecessary.
Therefore, it is required to measure the electrostatic capacitance with high directivity in a specific direction.